Fix few GCC9 warnings:
thirdparty/assimp/include/assimp/material.inl: In member function 'aiReturn aiMaterial::Get(const char*, unsigned int, unsigned int, aiColor3D&) const':
thirdparty/assimp/include/assimp/material.inl:176:33: error: implicitly-declared 'aiColor3D& aiColor3D::operator=(const aiColor3D&)' is deprecated [-Werror=deprecated-copy]
176 | pOut = aiColor3D(c.r,c.g,c.b);
modules/dds/texture_loader_dds.cpp:167:50: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
167 | if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("DXT1")) {
| ^
[ 28%] modules/dds/texture_loader_dds.cpp:170:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
170 | } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("DXT3")) {
| ^
modules/dds/texture_loader_dds.cpp:174:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
174 | } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("DXT5")) {
| ^
modules/dds/texture_loader_dds.cpp:177:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
177 | } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("ATI1")) {
| ^
modules/dds/texture_loader_dds.cpp:180:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
180 | } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("ATI2")) {
| ^
modules/dds/texture_loader_dds.cpp:183:57: error: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Werror=sign-compare]
183 | } else if (format_flags & DDPF_FOURCC && format_fourcc == PF_FOURCC("A2XY")) {
| ^
thirdparty/assimp/include/assimp/material.inl: In member function 'aiReturn aiMaterial::Get(const char*, unsigned int, unsigned int, aiColor3D&) const':
thirdparty/assimp/include/assimp/material.inl:176:33: error: implicitly-declared 'aiColor3D& aiColor3D::operator=(const aiColor3D&)' is deprecated [-Werror=deprecated-copy]
176 | pOut = aiColor3D(c.r,c.g,c.b);
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